The baboon is a spontaneously ovulating animal during the entire period of the year. The midcycle LH peak appears prior to ovulation and an estrogen peak is associated with the LH peak in plasma. Luteinization of corpus luteum and progestin secretion follow ovulation. Complete deafferentation of the basomedial hypothalamus tends to suppress the ovulatory cycle and follicular development as judged by plasma level of estrogen. Bilateral lesion of medial forebrain bundle at the level of lateral preoptic area tends to alter the preiodicity of ovulatory and menstrual cycles and also to suppress follicular development as judged by plasma level of estrogen. Localized deafferentation of posterior hypothalamus may not have any significant effect on ovulatory and menstrual cycles.